Conventional acoustic wave imaging systems use a one dimensional (1-D) array of electro-acoustic transducers, for example, a 1×100 array, and have been configured to achieve linear, curved linear and sector scanning. Coherence in the transmission and receipt of acoustic signals is achieved by the utilization of delay devices in the signal processing channels. Present one dimensional systems are disadvantageous due to (1) the manner in which they are constructed and (2) inherent limitations in their scanning capabilities. With respect to the manner in which they are constructed, one disadvantage is that the use of delay elements,  and related electronics adds considerably to the cost of one dimensional systems. With respect to inherent limitations, one dimensional scanning systems are disadvantageous in that they only provide two dimensional images.
To increase diagnostic capabilities it is desirous to have an acoustic imaging system that scans in two dimensions and thus produces a 3-D image. A problem with applying current 1-D technology to 2-D array imaging is that a vast number of electrical connections and processing electronics are required to serve an array of practical size. For example, a 100×100 array would have 10,000 individual transducers. Standard technology would require 10,000 electrical connections and processing channels. At an approximate cost of $100 per channel, such a system would require an outlay of $1M merely for channel electronics. In addition, if per channel power consumption is approximately 0.1 watt, then the system power requirement becomes at least 1 KW.
As a result of the disadvantageous aspects of providing large numbers of processing channels, current research efforts are directed towards achieving high performance with fewer array elements. Two prior art approaches are (1) the use of a two dimensional array with a reduced number of columns, termed a 1.5-D array, and (2) a thinned 2-D array.
A typical embodiment of a 1.5-D array is a 100 row×3-5 column array. Due to reduced aperture, 1.5-D arrays may not offer the increase in elevation resolution that will justify their added expense and complexity. Furthermore, research has shown that the use of aberration correction with 1.5-D arrays may not improve the image quality over that obtained using correction with a 1-D array.
In a thinned array, the number of array elements and associated electronics is reduced to several hundred by judiciously using only a selected number of transducers throughout the array aperture. This approach, however, has lead to significantly higher sidelobes in the beam profile of the system, compared to sidelobes in a beam profile for a full 2-D array. Thus, these systems are not suitable for such common uses as medical diagnostic imaging and the like which requires low and extremely low level sidelobes.
It should also be noted that the prior art does include 2-D annular arrays. These arrays are formed of concentric annual rings. They produce only a single ray, and while they perform dynamic focusing, they do not provide sector scanning. Scanning is achieved by physically moving the arrays.
In view of the foregoing, it should be apparent that a need exists in the art for both (1) a more economically constructed one dimensional scanning system, and (2) an acoustic wave imaging system that provides the high degree of resolution achievable with a full 2-D array, while reducing the number of processing channels and other circuitry associated therewith, amongst other needs.